Update. See some of the recent progress & work with the inlet manifold and carby 
here 
 
I found today, that after filling up the car with 95 RON (usually I just put 91 in) and giving it a good blast through the gears, the car began revving strong through the rev range with no stuttering.  
 
As my mate has recently acquired a cheap disco 1 as his first 4wd, we thought we would take it for a test run with my rangie on the Mundaring powerlines. 
 
It was a hot day 30+. The rangie did not take long to get pretty hot (3/4 of stock temp gauge) and began ****ing a little bit of coolant out the overflow.
The car occasionally stalled both on obstacles and 'normal' driving whilst it was hot, then refused to even try to tick over. Even putting a wire straight from the positive terminal of the battery to the starter motor - nothing would happen. 
 
Would this be a starter issue, or an ignition issue? Either way, I would have to wait for the car to cool down a bit before it would turn over/start.
 
In regards to the cooling, the car has 2 electric radiator fans that are wired up to be 'always on' when the ignition is turned on. I think one is orientated to pull air through it, and the other is the other way round. Now I think about it, shouldn't both be pulling air through the radiator? 
I had the radiator re-cored within a year or so ago, but with all the pulling apart and putting back together lately, the coolant is probably not at the right ratio (would be a bit weak). The thermostat is fairly new also. 
Any ideas as to why it is getting so hot, and any suggestions as to how I could help reduce this problem? Almost considering putting air vents in the bonnet to help lower under bonnet temps.... The exposed exhaust headers could also be a problem.